In petroleum exploration it is important to know accurately the pressure of oil and gas bearing formations penetrated by bore holes. For this purpose, there has been available for many years various types of bottom hole pressure gauges. Some pressure gauges include recording means within the gauge itself. The gauge is lowered into the hole at the end of a wire line. After the pressure recording is made, the gauge is retrieved and a reading made from the recording produced by the gauge while in the hole. Others have provided gauges for transmitting signals by way of a conductive cable to the earth's surface where the signals are utilized for ascertaining the pressure in the bottom of the bore hole.
The present invention is directed towards improvements in the latter type of pressure gauges and provides a gauge for lowering into a bore hole which penetrates a subterranean formation, the gauge being lowered by a conductive cable. The gauge functions to generate an A.C. signal, the frequency of which is indicative of the detected pressure of the subterranean formation.
One of the difficulties experienced with known pressure gauges of the kind which provide an A.C. signal readout transmitted to the earth's surface is that of maintaining accuracy of calibration as temperature changes.
Another difficulty experienced with known pressure gauges is that of maintaining accuracy of calibration. Down hole gauges must be lowered for a great distance, usually several thousand feet through a cased or uncased bore hole, to the bottom of a well. This must, for purposes of economy, be done as rapidly as possible. The gauges are therefore subjected to very rough treatment and yet they must be able to detect and remotely read out pressure to a high degree of accuracy. It is an object of this invention to provide a remote indicating pressure gauge which is constructed in such a way as to provide accurate pressure indication in spite of the rough handling and treatment to which such gauges are subjected.
Another object of this invention is to provide a remote reading pressure gauge, including improved means of detecting very small changes in pressure.
Another object of the present invention is to provide a bottom hole pressure gauge, including improved means of maintaining the accuracy of the gauge, particularly with respect to providing means of temperature compensation.
An additional object of this invention is to provide a remote reading bottom hole pressure gauge utilizing a capacitive type pressure detector including improved means for constructing the gauge for affording greater stability.
These general objects as well as other and more specific objects of the invention will be fulfilled in the following description and claims, taken in conjunction with the attached drawings.